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Thursday, October 25th, 2012.docx

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York University
Natural Science
NATS 1840
Carol Bigwood

Science, Technology and the Environment (SC NATS 1840A) – th Thursday, October 25 , 2012 Readings: 4.4, 4.5 Bulk of test covers Biogeochemical Cycles chapters 6 and 7, 3.3-3.7, 4.4, 4.5, 4.7, same format Biogeochemical Cycles part 3 – Energy Flow The Sun (Our source of energy) All of the energy available on Earth comes to us from the Sun. Facts about the Sun:  Size: 110 x Earth (Diameter)  Mass: 330,000 x Earth  Temp: 6000 degrees (surface) 10^7 degrees (core)  Composition: 90% Hydrogen 10% Helium  Energy source: Hydrogen fusion Sun’s power output varies continuously, but with some regularity.  11-year sunspot cycle correlated with solar output  Brightness (output) on a long term increasing trend; has probably rise by 25% since protostar phase. When supply of hydrogen runs out, Sun will die out and become a white dwarf in about 5 billion years. Earth (our home): Distance from Sun: 150,000,000 km Diameter: 12,745 km Mass: 5.9 x 10^24 kg Age: 4.6 billion years Lithosphere: solid rock crust floating on a liquid interior Hydrosphere: Temperature allows liquid water (71% of surface) Atmosphere: Mainly nitrogen (78%) and oxygen (21%) Solar Energy Received: Earth intercepts only a fraction of Sun’s total power output: An average about 1360 W/m^2 (the solar insolation) at top edge of atmosphere. Most of this energy is delivered in the form of visible light. Amount of solar energy that reaches surface and is absorbed by planet also depends on:  Albedo  Chemical composition of the atmosphere. Albedo: Amount of power reflected away from the Earth (or any planet), expressed as fraction of incident power. Depends on nature of surface and of atmosphere Albedo = (Power Reflected) / (Power Received) High albedo  more power reflected, less power absorbed, cooler (all else being equal) Clouds and ice have high albedo; water, rocks, and forests have low albedo. Earth’s average albedo: about 30% Chemical Composition of the Atmosphere A given gas allows EM radiation (light) to pass through at some frequencies, but strongly absorbs others. Some atmospheric gases strongly absorb the same range of infra-red EM frequencies which the surface of the Earth Emits as a result of its temperature Greenhouse Gases Example: Water Vapour, Carbon dioxide, methane, etc… Ozone in the upper atmosphere also strongly absorbs light at ultra-violet frequencies The Greenhouse Effect: Without greenhouse gases average surface temperature would be about 33 degrees colder than it actually is Because of atmospheric greenho
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